Recently, equipment such as a car air conditioner has had higher qualities. Accordingly, rotary variable resistors used for controlling such equipment have been required to output resistance values more precisely.
A conventional rotary variable resistor used for such equipment is described with reference to FIGS. 6 to 7.
FIG. 6 is a sectional view showing a conventional rotary variable resistor; and FIG. 7 is an exploded perspective view thereof. Conventional rotary variable resistor 61 includes case 5 made of an insulating resin, rotator 6 and slider 7.
Case 5 has resistive substrate 1 provided with circular center hole 1A at the center thereof and made of a phenolic paper laminated sheet or a glass epoxy resin laminated sheet. On the upper surface of resistive substrate 1, horseshoe-shaped resistive element 2 is formed at the outer circumferential side and ring-shaped conductive portion 3 is formed at the inner circumferential side of resistive substrate 1. Resistive element 2 and conductive element 3 are concentrically formed by screen printing, and the like. On both ends of resistive element 2 and on a lead provided outwardly from conductive portion 3, terminals 4A, 4B and 4C are fixed to resistive substrate 1 by caulking. Thus, terminals 4A, 4B and 4C are electrically coupled to resistive substrate 1.
Case 5 has fitting hole 5A provided at the center of a cavity with an open top in such a manner in which the position and size of fitting hole 5A is adjusted to those of center hole 1A of resistive substrate 1. Case 5 is formed by insert molding resistive substrate 1 so that resistive element 2 and conductive portion 3 are exposed to the inner bottom surface of the open portion. Therefore, resistive substrate 1 is fixed to case 5, and terminals 4A, 4B and 4C protrude outward from the side wall of case 5, respectively.
Rotator 6 has oval through hole 6A at the center thereof, and includes disk-shaped flange 6B in the upper part thereof and cylindrical shaft 6C in the lower part thereof. To the lower surface of flange 6B, slider 7 is fixed. Slider 7 is brought into sliding contact with resistive element 2 and conductive portion 3 formed on resistive substrate 1. Cylindrical shaft 6C is inserted into center hole 1A of resistive substrate 1 and fitting hole 5A of case 5 from the upper part, and caulked thereto in a state in which a thin-walled lower end portion of cylindrical shaft 6C is expanded outward. Thus, rotator 6 is rotatably combined with case 5.
An operation of rotary variable resistor 61 configured as mentioned above is described. When rotator 6 is operated by using a rotation assisting tool (not shown) inserted into oval through hole 6A of rotator 6, slider 7 fixed to the lower surface of flange portion 6B slides on resistive element 2 and conductive portion 3 of resistive substrate 1. Then, output resistance values corresponding to the contact positions of slider 7 in rotation operation are obtained from terminals 4A, 4B and 4C.
Note here that the above-mentioned conventional technology is disclosed in, for example, Japanese Patent Unexamined Publication No. 2003-124008.
However, in conventional rotary variable resistor 61, due to variation of resistance element portion 2 formed on resistive substrate 1 by printing or deviation in the combination of the components, and the like, deviation between an intended resistance value at a desired rotating angle and a output resistance value is likely to occur.
On the other hand, from manufacturers of vehicle-mounted equipment and AV equipment, there are increasing demands for strict output precision with less deviation. However, when higher precision is intended to be realized, yield is deteriorated, thus increasing the manufacturing cost.